1. Field of the Invention
The present invention relates to demodulation of radio signals from a transmitter having collocated transmit antennas, and more particularly to distinguishing signals transmitted in a MIMO timeslot from multiple antennas.
2. Description of Related Art
Bursts belonging to a Time Division Multiple Access (TDMA) system consists of a training sequence and a guard period in addition to the data payload. The training sequence may occur at the start of the burst (preamble), middle of the burst (midamble), or end of the burst (postamble). In general there may be multiple training sequences within a single burst. The training sequence used in a mobile radio system is typically a midamble. The guard period is placed at the start and/or end of a burst to reduce interference arising from dispersive channels.
In Code Division Multiple Access (CDMA) systems, multiple bursts may be transmitted simultaneously over a Time Slot (TS), each spread by a distinct signature sequence or channelization code. In a Time Division-Code Division Multiple Access (TD-CDMA) system, such as UTRA TDD, a mapping between a channelization code and a midamble is defined such that the channelization code of a burst may be derived implicitly using its midamble sequence.
However, although training sequences may facilitate reception, the use of training sequences tends to be suboptimal in many communication systems. Particularly, in MIMO systems a suboptimal performance tends to be achieved.
Hence, an improved system for generating signals in a MIMO timeslot would be advantageous and in particular a system allowing increased flexibility, reduced complexity and/or improved performance would be advantageous.